Fluid pipes are extremely inconsistent

I have a raffinery setup that should work but pipes say no

Here is what I have

|<-R1           |->R10
|<-R2           |->R11
|<-....         |->R12
|<-R7           |->R13
|<-R8           |->R14
|               |
(400/min)       |    
|____valve>_____|
  • R1-8 are producing 400/min total
  • R10-14 are consuming 400/min together

What's the problem: R10,11 and 12 only work on 40to80% efficiency because they don't get enough of the fluid. And the reason for that is that R1 to R4 complain that the pipe is full. So on one side the pipe is to full on the other it's too empty ... And in theory all should run on 100%

What I tried

  • using a pump where the valve is
  • with and without valve
  • resetting the system by filling up all piped plus R10-14 completely to prevent sloshing
  • replacing all cross sections so that pipes only go to the input of the cross section and not "into" it

Nothing helped. The flow at the valve is mostly 400 but then it plummizs to 20 for a few secs befor going back to 200 and then back to normal.

Wtf am I doing wrong?? Are pipe systems just broken?

Here is a picture of my headlift situation

https://preview.redd.it/tbkick00q11e1.png?width=1699&format=png&auto=webp&s=dbeb64e47232db87fda8d8bd14303a8dd0da454c